The present invention relates to the removal of coreless rolls of a stretch film wound up on a perforated mandrel, by means of which a cushion of pressurised air is generated to cause a radial expansion and compaction of the internal turns of the coils, allowing said coils to be slidably removed without frictional forces.
In particular, the invention is directed to a method as well as to a mandrel and a device for removing coreless rolls of a stretch film in winding machines, said method, mandrel and device being suitable for achieving a substantial reduction of the compressed air consumption.
The invention is suitable for winding and removing coreless rolls of stretchable plastic films, normally used for packaging of industrial products, for example for wrapping palletised loads or other similar applications, for which the demands for improving the production process, reducing the costs for winding and removing the rolls, as well as simplifying the management problems, appear to be always more important.
For the present invention, stretch film is a thin continuous web of plastic material, obtained by extrusion or co-extrusion of one or more layers, with thicknesses comprised for example between 10 and 80 microns, or higher.
Stretch films hold a preeminent position in packaging due to their excellent functional qualities; one of the characteristics that are distinguishing a stretch film from any other web material is its “cling”, that is the ability of the stretch film to adhere to itself creating a seal on the package.
Mechanical properties of a stretch film are also relevant in relation to the tear and pull resistance, with stretch values up to 100-140% and more, and a relatively low Young's modulus; use of stretch film in packaging have proved to reduce the amount of film consumption as much as 40-50%.
Furthermore use of correctly wound up coreless rolls of stretch-films having a number of compacted internal turns, which maintain a cylindrical shape of the rolls after the removal from the mandrel, that is suitably conformed to avoid any risk of implosion and deformation of their cylindrical shape, is a very relevant characteristic that makes the packaging and wrapping of palletized loads by stretch films, easier and faster, with significantly higher output. Therefore, the use of stretch films, in respect to other web materials and different technical fields, is very important.
Considering these characteristics, in particular the autoadhesive or cling property of the stretch films normally used in the packing field, the method, the mandrel and the device according to the present invention besides enabling the internal turns of the rolls to be compacted, that stabilises the shape and the diameters of said internal turns during the time, aid as well the rolls to be taken off and removed without friction from the winding mandrel, so as to achieve a substantial reduction of the pressurised air consumption and energy saving.